When were the broking at tau?

I just want someone to explain to me what happened before the old war. It was my understanding that the orokin sent the zaramin to taught to inhabit it but that failed... so.when did they get there afterwards like it's shown in the new trailer stuff? Did they leave earth and get to tau within a century or two after 1999 takes place? And if they where at tau then what was with the zaramin? Where was it going to before getting stuck in the void? I would really just like an explanation because the story so far leads be to believe there were living in tau and tried to get back to earth... but whatever I look up says they were never able to get to tau because the sentients started the war so they wouldn't mess up tau like they did earth